BOISE, Idaho (AP) Defensive back Dextrell Simmons is reluctant to call No. 21 Boise State's near-collapse in the second half against New Mexico four weeks ago a turning point.

Yet by nearly any measure since the Lobos rushed for 330 yards and put up 29 points in a second-half rally that fell short, the Broncos defense has been as tough as any in the nation at keeping foes out of the end zone and been the driving force behind the team's six-game winning streak.

The Broncos (6-1, 3-0 Mountain West) have muscled their way into top 10 slots for several defensive categories, including pass defense (158 yards per game), pass efficiency defense (95.6) and points allowed (13.5). Their 22 turnovers rank second among FBS schools, three behind takeaway leader SMU, and three times this season they have held opposing quarterbacks to fewer than 100 yards through the air.

Simmons said the motivation for the team is simple: A collective fear of failure.

"It's basically coming from not wanting to fail," said Simmons, who is tied for fifth on the team with 31 tackles. "New Mexico was our worst defensive game. After that, we were like `it can't happen again.'"

So far it hasn't.

Boise State's last three opponents have only scored 31 points collectively, and the defense should actually get credit for pitching a shutout in a 32-7 victory over UNLV on Saturday since the only Rebels touchdown came on a fumble return.

The defense has held opponents scoreless in the first half in each of the last five games, giving Boise State's offense plenty of opportunity to build leads and force opposing offenses to discard their game plans. The defense is also doing its share to put points on the board.

Against the Rebels, cornerback Jerrell Gavins scooped up a fumble and scampered 16 yards for a touchdown to give Boise State a 25-0 halftime edge. The defense also accounted for the only touchdowns in a 17-13 season opening loss at Michigan State and a 7-6 victory two weeks later against BYU.

The performance of the defense has been a pleasant surprise.

The defense was expected to be in a rebuilding mode following the graduations of eight starters, including players like Shea McClellin, Billy Winn and Tyrone Crawford, all stalwarts on the defensive line who are now playing the NFL.

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But as Simmons and his teammates have pointed out for weeks, Boise State's rotation system enabled many of the players wreaking havoc this season to get valuable experience last year. And those lessons are paying big dividends now.

"This year the standards are the same. We still want to win ... and be the best defense," said Simmons. "Last year we had big-name guys and you come in and think there are no big-name guys this year. But it's the same guys that were under those big-name guys and now they're just taking it to a whole new level."

The Broncos, who lead the conference, are getting ready to travel to Wyoming on Saturday. The Cowboys (1-6, 0-3) will be without head coach Dave Christensen, who was suspended for one week and fined $50,000 Monday for his actions following an Oct. 13 loss to Air Force.

Christensen confronted Falcons coach Troy Calhoun on the field after Air Force's 28-27 victory. He accused the Falcons of faking an injury to their starting quarterback in the fourth quarter so they could set up the next play without taking a time out. Air Force took the lead on the next play when backup quarterback Kale Pearson scored on a bootleg.